Tree peony is a unique oil plant resource in China, and tree peony seed oil is one of the healthy edible oils with a very promising future. However, the main oil tree peony cultivars promoted in China are Paeonia ostii ‘Fengdan’ and Paeonia rockii. In order to explore new oil tree peony cultivars, 68 tree peony cultivars were investigated and cultivars with oil potential were selected by cluster analysis and grey relational analysis (GRA) in this study. The results demonstrated that the 68 cultivars varied significantly in terms of agronomic characteristics (p < 0.05), with the coefficient of variation in seed yield per plant reaching a high of 75.36%. The oil content of 46 cultivars was higher than ‘Fengdan’ (20.87 ± 0.26%) and ‘Zibanbai’ (21.24 ± 1.01%), while the alpha-linolenic acids and total unsaturated fatty acid contents of 26 cultivars were higher than ‘Fengdan’ (39.79 ± 1.13% and 88.99 ± 0.47%) and ‘Zibanbai’ (40.51 ± 0.09% and 93.59 ± 0.09%). Finally, three cultivars with better integrated traits were selected by cluster analysis and grey relational analysis (GRA), comprising of ‘Changshoule’, ‘Xianchizhenghui’, and ‘Yupantuojin’. The contents of alpha-linolenic acids and total unsaturated fatty acids in ‘Changshoule’ (47.98 ± 0.17% and 93.60 ± 0.08%), ‘Xianchizhenghui’ (49.44 ± 0.63% and 93.80 ± 0.06%), and ‘Yupantuojin’ (40.46 ± 0.26% and 93.58 ± 0.06%) were higher than that of ‘Fengdan’ (39.79 ± 1.13% and 88.99 ± 0.47%). In general, these cultivars can be used as hybrid parental materials for breeding new excellent oil tree peony cultivars.

Tree peony (Paeonia section Moutan DC.) is a traditional ornamental flower of China, which has thousands of varieties with different flower colors and types after a long history of natural selection and artificial breeding. However, tree peony is a perennial woody plant with a long breeding, and there are still significant challenges to accelerate the process of genetic improvement of important ornamental traits. In this study, a total of sixteen primer pairs with high polymorphism and good universality were selected from the initial pool of 115 SSR markers. The SSR marker set was derived from published papers on the genetic linkage map and association analysis of tree peony. Furthermore, we conducted a genetic diversity and population structure analysis on 322 tree peony cultivars using molecular markers with functional. These SSRs amplified a total of 391 alleles, the average number of different alleles was 5.113 alleles across all loci. The average Shannon’s information index, gene diversity and polymorphism information content were 0.842, 0.532, and 0.503 over all loci, respectively. Population genetic diversity analysis indicated that the average expected heterozygosity of the total population was larger than the observed heterozygosity, showing the presence of a certain degree of heterozygous deletion phenomenon. The Japan varieties had the richest diversity with the highest H (0.508) and PIC (0.479) values. The Zhongyuan varieties showed the greatest variation may be related to its longstanding cultivation history. Moreover, the STRUCTURE and principal coordinate analyses indicated that 322 tree peony individuals from five populations were grouped into two clusters. An analysis of molecular variance demonstrated significant genetic diversity among different populations. This research may contribute to the sustainable management, conservation, and utilization of tree peony resources.